This invention relates generally to circuit interrupting apparatus, and more specifically to a high-voltage, gas-insulated puffer-type circuit breaker having the interrupting unit disposed within an insulating casing.
High voltage power circuit breakers today are generally grouped into two classes: live tank and dead tank designs. A dead tank circuit interrupter generally is one in which the interrupting unit, with its separating contacts, is disposed within an electrically grounded metal tank which then is disposed on or at physical ground level. A live tank design, on the other hand, has its interrupting unit, with its separating contacts, disposed in an insulating housing which then is supported upon an insulating column. This difference in configuration is partially the result of the various regulatory codes in effect in both the United States and in foreign countries, which codes typically specify that the base of the insulators should be at a definite distance to earth independent of the voltage class considered, thereby implying that the lowest live part has to be at a distance to ground dependent on the voltage class and basic impulse level prescribed. In the case of the dead tank circuit breaker, the terminals correspond to the highest point of the circuit breaker and the lowest point of live parts. Conversely, in a live tank circuit breaker, these dimensions can vary depending on the interrupter chamber configuration: horizontal, oblique, vertical. These dimensions often define the height of the substation steel structures required, and considerable savings in substation structure costs can often be realized with a dead tank concept.
The dead tank circuit breaker also exhibits numerous advantages over the live tank circuit breaker. For example, the built-in current transformers which can be utilized with the dead tank circuit breaker provide significant economical advantages. Similarly, the dead tank circuit breakers present simplicity of erection and easy insulation coordination to ground, exhibit better size and withstand characteristics due to having a lower center of gravity and lighter live parts, and the interrupter mechanical support insulator and operating rod in the dead tank interrupter can be of small dimensions and not be subjected to ambient pollution.
The live tank circuit interrupter also has numerous advantages. For example, generally the cost of the circuit breaker itself is smaller for the live tank circuit breaker than for the dead tank circuit breaker. Furthermore, the live tank circuit breaker generally uses a smaller quantity of gas than does a dead tank circuit interrupter, for the same voltage classification and withstand levels. Furthermore, an important advantage of the live tank circuit breaker is the electric field distribution between separated contacts when the breaker is in the open position. The electric field stresses between the contacts in the open position for the live tank circuit breaker are significantly less concentrated for the live tank design than is the electric field configuration for the dead tank design.